Melamine-formaldehyde derived porous carbons for adsorption of CO₂ capture

In this work, we report carbon adsorbents obtained from high nitrogen content melamine-formaldehyde resin as starting material and mesoporous zeolite MCM-41 as template through nanocasting technique. To synthesize different carbon structure adsorbents with improved textural and surface properties, the material undergo carbonization followed by physical activation under CO₂ atmosphere at different temperatures. Characterizations of the adsorbents using SEM, TEM, XPS, nitrogen sorption, CHN, TKN, and TPD have been carried out. Characterization results reveal the development of nanostructured carbon adsorbents with better texture and surface properties as compared to the sample prepared by direct carbonization. Sample prepared at carbonization-activation temperature of 700 °C shows highest basicity, surface area (193.28 m² g^-1) and pore volume (0.32 cm³ g^-1). Performance evaluation of adsorbent was performed thermo gravimetrically at different temperatures and concentrations and was found that the adsorbent synthesized at 700 °C exhibit highest CO₂ uptake of 0.93 mmol g^-1 with nitrogen content of 22.73%. It was found that both surface area and nitrogen functional group have a major impact on adsorption capacity. Physiosorption process was confirmed by a decrease in adsorption capacity with increase in temperature. Three kinetic models and isotherms were used in this study and found that fractional order kinetic model and Freundlich isotherm best fitted with the experimental data. Isotherm study depicts the heterogeneous nature of adsorbent surface. Adsorbent exhibited complete regenerability and was stable over four adsorption-desorption cycles. Low value of isosteric heat of adsorption of 15.75 kJ mol^-1, indicates physiosorption process. Negative value of ΔG⁰ and ΔH⁰ confirms spontaneous, feasible and exothermic nature of adsorption process.